A synthetic approach to the pyrazole carboxylic acid derivative of the formula I has been described in scheme 3 of the Int. Patent Publication WO 2011/117264 applying a method disclosed in Hanzlowsky et al., J. Heterocyclic Chem. 2003, 40(3), 487-489.
However, under the acid-catalyzed cyclocondensation conditions described, besides of the desired isomer, also a substantial amount of the undesired N−1 substituted isomer was formed. In many cases, especially on larger scale, this undesired isomer is the major product in the reaction mixture with ratios of up to 70:30 in favor of the undesired isomer, leading to isolated yields of ca. 30% of the undesired isomer, along with ca. 25% of the desired isomer.

Separation of the desired from the undesired isomer, e.g. in the example described above, could only be achieved by applying chromatography techniques. Such methods are not desired for technical scale synthesis, due to economic and ecologic considerations.